The concept of air flotation in wastewater treatment is to use the hydrophobic particles in wastewater to form highly dispersed microbubbles in water, so that the pollutants in wastewater are adsorbed on the bubbles, and the pollutants float to the surface with the bubbles, thus forming a three-phase mixture of water, gas and particles, and thus realizing the separation of pollutants and water.

Wastewater treatment is crucial for national livelihood and public health, while also promoting sustainable water resource utilization. Based on the properties, types, pressurization methods, and purification levels of suspended solids in wastewater, treatment methods are generally categorized into three types: (1) Full-process dissolved air flotation (DAF) 111. This method involves injecting air before or after pump pressurization, with a large dissolved air volume that enhances contact opportunities between suspended solids and bubbles. The entire wastewater is then pressurized by water pumps. In the dissolved air tank, air dissolves into the wastewater, which is subsequently pumped to the flotation tank through a pressure relief valve. Numerous small bubbles form in the wastewater, adhering to emulsified oil or suspended solids, creating floating scum on the water surface. Scrapers collect the scum into a scum tank, which is discharged through a scum pipe. The treated wastewater is then discharged via an overflow weir and outlet pipe. Under the same treatment volume, this method requires a smaller flotation tank compared to partial recirculation DAF, thereby reducing capital investment. However, since all wastewater passes through the pressure pump, it increases the emulsification degree of oily wastewater. Additionally, the required pressure pump and dissolved air tank are larger than those needed for the other two processes, resulting in higher investment and operational energy consumption.

(2) Partial dissolved air flotation (DAF) 1111 This method involves pressurizing and aerating only a portion of the wastewater, requiring less pressure pump capacity and lower energy consumption compared to the full-process flotation method. The remaining wastewater flows directly into the flotation tank, where it mixes with the aerated wastewater. During this process, the amount of emulsified oil caused by the pressure pump is relatively lower than in the full-process DAF method. The flotation tank size is similar to that of the full-process method but smaller than that of the partial recirculating DAF method.

(3) Partial Recirculation Dissolved Air Flotation Method 111 This technique involves extracting a portion of the wastewater, removing oil, and then recirculating the treated water to the next stage: pressurization and dissolved air injection. The reduced water volume during pressurization minimizes energy consumption. After depressurization, the wastewater flows directly into the flotation tank. Unlike the previous methods, this process does not promote emulsification, resulting in less flocculation in the effluent and better floc formation. To enhance treatment efficiency, coagulants or flotation aids are typically added to the wastewater, which is then mixed with oily wastewater from the flocculation tank for flotation. The recirculation rate of this method generally ranges from 25% to 100% of the oily wastewater volume. The flotation tank requires a larger capacity compared to the other two methods.